Scavenging and charging of twocycle engines



Oct. 30, 1934. E. BL POLL ISTER V 1,973,816

I SCAVENGING AND CHARGING OF TWO-CYCLE ENGINES Filed Oct. 22, 1931 i -n34 I j a 57 l 35 I 25 3 WfiNVENTOR.

67 TORNEY Patented Oct. 30, 1934 SCAVENGING AND CHARGING OF TWO- CYCLEENGINES Edward B. Pollister, St. Louis, Mo., assignor to .Busch-SulzerBros.-Diesel Engine Company,

St. Louis, Mo.,

a corporation of Missouri Application October 22, 1931, Serial No.570,289

7 Claims.

My invention relates to two-cycle internal combustion engines havingpiston-controlled scavenging-air and exhaust ports, and moreparticularly to injection-type or Diesel engines of I this class, and isparticularly suited for socalled high speed Diesel engines, normallyoperating at speeds of 400 R. P. M. and higher and intended to be usedat variable loads and speeds.

10 The object is to improve the scavenging and charging process of suchengines, and more particularly the scavenging, so that the cylinder willbe thoroughly evacuated of. combustion products notwithstanding the highspeed and II the consequent shortness of the periods available for airadmission, such periods being too short for adequate scavenging andcharging by the customary .simpler scavenging and charging processheretofore employed.

I have discovered that better scavenging than heretofore, and especiallybetter scavenging of the upper or head ends of the cylinders, andimproved charging and supercharging, are obtainable by the Joint use ofhigh and low pressure air, where the low pressure air is admittedsubstantially as and while the exhaust port or ports is or are open andthe high pressure air is admitted as soon as the pressure within thecylinder has fallen sufllciently to receive it and is continuedthereafter until, at least, the inflow of low pressure air is stopped.Especially for better charging and for super-charging however, theadmission of the high-pressure'air may be (and usually it is) continuedfor some time after the inflow of low pressure air is discontinued. Ihave discovered also that such a scavenging and charging, orsuper-charging, process is adequate for the high speed engines beforementioned, and especially is well suited for engines, of the kindindicated, designed for the higher speeds now contemplated for Dieselengines, say from 400 to 1000 R. P. M. and wherein it is desirable toeliminate all valve gearing in the vicinity of the scavenging andcharging ports.

I have found it is important that the highpressure air be admitted assoon as the cylinder pressures have fallen below the pressure of thehigh-pressure air, and according to my invention, I use automatic, orself-opening, valves to control the high-pressure ports, i. e. valvesoperated by the difi'erence between the pressure withinthe cylinder andthe pressure of the highpressure air, so that there may be no delaywhatsoever, under any condition oi speed, load or fuel control, in theintroduction of the highpressure air after the cylinder pressure hasfallen sufficiently to admit it. For the higher-pressure air, I haveobtained excellent scavenging at speeds above 400 with pressure aroundfour pounds above atmosphere; however, the pressure of the high-pressureair may vary with the construction of the ducts and ports, and it mayvary with changes in the engine speed, etc., and may also beconsiderably greater than four pounds above atmospheric pressure,especially if considerable supercharging is to be accomplished. Thelow-pressure air is admitted at about the same time, and, for example,at about the same pressures as heretofore customary when scavenging withlow-pressure air alone, this including of course maintaining the airpressure constant outside the ports to about the same degree at least ashas heretofore been customary in practice.

I employ entirely separate ports in the cylinder side walls for the highand low pressure airs. I have found too that it is desirable to locatethe high-pressure air ports somewhat nearer the head ends of thecylinders than the lowpressure ports. Further, minimum power consumptionin air compression is obtained by providing separate sources for thehigh-pressure air and the low-pressure air, with separate ducts andreceivers for conveying the high-pressure air and the low-pressure airto their respective ports.

The accompanying drawing illustrates the invention diagrammatically,Figure 1 representing I a section of a cylinder of a two-cycle Dieselen- 90 gine with my invention applied in a form employing (as preferred)separate sources for the high-pressure and the low-pressure air, andFigure 2 representing a similar section but showing the use of a singleinitial source for both the high-pressure and the low-pressure air.

In Fig. 1 the engine cylinder is shown at 1 andits piston at 2; themember 3 will serve to indicate the fuel injection valve whereby fuel isinjected into the cylinder at or near the sub- 100 stantial completionof the compression stroke, as in ordinary Diesel engine practice.Pistoncontrolled exhaust ports are shown at 4. At 5 are shown a numberof air inlet ports for the low-pressure air, likewise opened and closedby the reciprocating piston. As in ordinary lowpressure scavenging,these low-pressure air ports 5 are so placed that the piston begins touncover them only after the exhaust ports 4 have been so far opened thatthe cylinder pressure has low-pressure air.

fallen below the pressure of the low-pressure air, and the completeopening ofthese inlet air ports 5 takes place at about the end of thepower or working stroke as indicated in Fig. 1. At 6 are a number of'-high-pressure air inlet ports, these being placed (in accordance withthe preference before expressed) nearer the head end of the cylinderthan the low-pressure ports 5. The high-pressure air port or ports 6may. be, and usually will be, so placed as to be uncovered by thepiston, in part at least, prior to the beginning of the opening of theexhaust ports 4, in order that the high-pressure air may have adequatemeans of access to the interior of the cylinder at the instant thepressure within the cylinder has fallen sufllciently to admit theentrance of this high-pressure air; and so as to be closed by the pistononly after the exhaust ports have been closed, in order to provide forthe entrance of some charging air (and super-charging air if desired)after the closing of the exhaust ports on the compression strokes. Theblower '7 and blower 8 represent the separate sources for thelow-pressure air and the highpressure air respectively, these beingseparately piped to the low-pressure air receiver 9 and thehigh-pressure air receiver 10 at the engine.

As before indicated, my invention contemplates the use of automatic orself-opening valves to prevent entry of the cylinder combustion gas intothe high-pressure air duct or ducts prior to the time when the cylinderpressure has fallen below the pressure of the highpressure air. InDiesel engines operating at the high speeds to which this inventionparticu' larly relates, it is found impractical, if not impossible toprevent such entry without unduly abbreviating the period of scavengingwith highpressure air, unless the valve is closed by the pressure of thecombustion gas itself; attempts to time a positively operated valve soas to obtain the same length of period of high-pressure scavenging as isobtainable with gas-operated self-opening valves, result in blow backsand explosions of dangerous character. Such self-.

closing valve is indicated at 11, consisting of a.

number of louvers or light and easily movedv horizontally-pivoted vanesopening toward the cylinder when the pressure in the receiver 10 exceedsthe pressure within the cylinder, but closing quickly one against theother when the pressure within the cylinder predominates.

It will be observed that the descent or outward movement of the piston 2during each power stroke, by uncovering the exhaust ports 4 ultimatelypermits the pressure within the cylinder to fall to such a degree thatthe pressure of the air within the higher-pressure receiver 10predominates and as soon as this happens the highpressure air begins toenter the engine cylinder through the then partially or fully open airports 6. After the exhaust ports have been opened, the piston uncoversthe low-pressure ports 5, and thereupon low-pressure air also enters thecylinder, the higher-pressure flow continuing. The cylinder isscavenged, therefore, and recharged with combustion air by the jointaction of the high-pressure air and the On the return of the piston. onthe next compression stroke, the low-pressure ports 5 are first closed;thereafter the exhaust ports are closed, and the high-pressure ports arenot completely closed until some time after the closing of the exhaustports; during this interval between the closing of the exhaust and Inthis two-source process there is, it will be observed, minimum powerconsumption in compressing the airfor scavenging and charging orsuper-charging, inasmuch as only the highpressure air is compressed tothe higher pressure, the air for the receiver 9 being compressed to onlythe lower pressure.

My invention is not limited however to using separate sources for thehigh-pressure and the low-pressure air, although that is moreeconomical, but one source alone may serve, as indicated in Fig. 2, thepressure being reduced for the low-pressure receiver, by throttling orother means. The cylinder 21, piston 22, fuel injection valve 23,exhaust ports 24, low-pressure air inlet ports 25, high-pressure airinlet ports 26, low-pressure air receiver 29, high-pressure air receiver30, and the automatic self-opening valve or louvers 31 (opening towardthe cylinder) will be recognized from and correspond to. similar partsin Fig. 1. The single blower 34 serves to provide air at thehigher-pressure needed for the high pressure air inlet ports 26, andalso air in suflicient volume to supply the low-pressure ports 25 aswell. By passing a limited quantity of this air into the low-pressurereceiver 29,

through a sufiiciently restricted passageway or stricted .as to maintainwithin the receiver 29 1 only the lower pressure contemplated therefor.Obviously my invention is not limited to a passage or connection fromthe high-pressure receiver to the low-pressure receiver of a fixed andinvariable area. The air receivers 9 and 10 and likewise the receivers29 and 30 will be understood to be common to and supply all thecylinders of a multicylinder engine, although only one cylinder has beenillustrated, the'capacity or air storage thus provided, plus thecontinuous flow of air from the blowers '7 and 8 (or from the blower 34and through the inter-receiver passages 35), serving to maintain the airpressures outside the engine ports during the scavenging periods, thatis to say, to keep these pressures constant at all times during thescavenging period to at least substantially the same receiver 30 and thedegree as has been the practice heretofore with cated, by way ofexample, by the deflector 37 on v the piston head, and shown partly insection in the two figures, and the forms and use of which,

in connection with scavenging by low pressure air alone, are well known.or this directing may be accomplished by the appropriate sloping of theport passages through the cylinder walls.

todowithsloping port In general, it will be understood that my inventionis not limited tothe exact operation and details '0! constructionillustrated and described above, except as particularized by the claims.

I claim:

i. In a two-cycle injection-type engine having piston-controlled exhaustand air inlet ports, means for supp ying both low-pressure air andhigher-pressure air to said air inlet ports, said means substantiallymaintaining the pressure of at least the low-pressure air during thescavenging operation, and an automatic valve, self-opening toward thecylinder when the pressure of the higher-pressure 'air exceeds hepressure within the cylinder, said valve controlling flow through the ethrough which said higher pressure air is passed into the cylinder.

1- In and for scavenging and charging the cylinders ot two-cycleinjection-type engines, a source-oflow-pressure air, a source orhigherpressure air, a duct communicating with andreceiving air from thesource or low-pressure, a duct communicating with and receiving air fromthe source ofhigher-pressure, anengine cylinder. apiston workingtherein, ports being provided'in thewall oi the cylinder, meansproviding 'a passage between said ports and the lowpressure duct; saidmeans, low-pressure duct and low-pressure source substantially!maintaining the pressure ot'the low-pressure air at said ports duringthe scavenging operation, other ports also being provided-in the wall ofthe cylinder, means providing a passage between said other ports andsaid higher-pressure duct, said other ports being located nearer thecylinder head than the first mentioned ports, and an automatic valvebetweenthe higher-pressure duct and its ports, said valve opening solelyby the pressure or the air toward theinterior oi the cylinder andclosing by the pressure of the cylinder contents.

3. The method oi'scavenging. and

Y cylinder "wherein the exhaust passes the cylinder tlrromh the wallfrom oithe injection-type 3 latter at a point relatively remote from thecylinder head, which consists in passing air under pressure into thecylinder through the cylinder wall at a point remote from the cylinderhead, and thereafter and while said air is continuing to pass into thecylinder also passing air under a substantially maintained lowerpressure into the cylinder at a point more remote from the head end ofthe cylinder, characterized by the fact that the entry or saidhigher-pressure air is begun on the instant that the pressure within thecylinder has fallen below the pressure of this air.

4. The subject matter of claim 1, characterized by the tact that saidmeans for feeding air includes separate blowers tor the air at thehigher-pressure and the air at the lowerpressure.

5. The subject matter or claim 1. characterized by the fact thatseparate ports are provided for the inlet of the higher-pressure air andthe inlet or the low-pressure. air to the cylinder.

6. The subject matter of claim 1, characterizcd by the factthat'separate ports are provided for the inlet of the higher-pressureair and the inlet of the low-pressure air to the cylinder, and by thefact that the said port or ports for said higher-pressure air entercloser to the cylinder head than said port or engine having and two setssaid inlet with conports for said low-pressure air.

7. A two-cycle injection-type piston-controlled exhaust ports ofpistonecontrolled air inlet p0 ports being respectively connected duitssupplied with air, one at a relatively low pressure and the other at ahigher pressure and the higher pressure air inlet ports being nearer tothe head end oi the cylinder than the lower pressure air inlet ports anda self-opening valve in the communication between said high pressureconduit and the higherpressure inlet ports adapted to pass said highpressure air to the cylinder instantly on the falling of the cylinderpressure below the pressure or said air.

EDWARD B. POLLIB'I'ER.

